1. Technical Field
The present application relates to an access controller which conducts arbitration between a number of bus masters that are attempting to access the same slave through a network of semiconductor buses.
2. Description of the Related Art
Some semiconductor integrated circuits have a system in which a bus master that needs to have a guaranteed access to a memory at a constant rate (which will be referred to herein as a “rate-guaranteed-class bus master”) and a bus master that issues a request to access the memory irregularly (which will be referred to herein as a “processor-class bus master”) share the same memory.
In such a system, it is difficult to predict exactly when the processor-class bus master issues an access request. That is why such a system needs a circuit for conducting arbitration to avoid contention between the access request issued by the rate-guaranteed-class bus master and the access request issued by the processor-class bus master. Some people disclosed a technique for providing an access controller which enables such an arbitrating circuit to respond much more quickly to that hardly predictable access request issued by the processor-class bus master.
For example, Japanese Patent No. 4485574 supposes a situation where while a rate-guaranteed-class bus master is accessing a shared memory, there is some transmission band available and the next access request is issued. According to the technique disclosed in Japanese Patent No. 4485574, by getting a preceding access done at a rate exceeding the one that has been set originally for the rate-guaranteed-class bus master, a margin is left for the next access to be carried out periodically. With such a margin left, when such a hardly predictable access request is issued by the processor-class bus master, the transmission band that has been allocated in advance to the rate-guaranteed-class bus master is shifted to the processor-class bus master. In this manner, such an almost unpredictable access request by the processor-class bus master can be responded to much more quickly, and therefore, the access can get done with a shorter time delay.